The Atomic Bomb.
This one powerful weapon has contributed to a new type of diplomacy across the globe and dictated a new standard in the way that wars are fought. Think about it. A dozen countries with the ability to end civilization at the touch of a button.
The bomb has the ability to create fear and mass hysteria. Just look at the 50's. Just look at terrorism today.
The technology has spawned new power sources and propulsion systems.